JP6197610B2 - Positive electrode active material, positive electrode and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a positive electrode active material, a positive electrode, and a lithium ion secondary battery.

Conventionally, a layered compound such as LiCoO ₂ or LiNi _1/3 Mn _1/3 Co _1/3 O ₂ or a spinel compound such as LiMn ₂ O ₄ has been used as a positive electrode material (positive electrode active material) of a lithium ion secondary battery. It was. In recent years, compounds having an olivine type structure typified by LiFePO ₄ have attracted attention. It is known that a positive electrode material having an olivine structure has high thermal stability at high temperatures and high safety. However, the lithium ion secondary battery using LiFePO ₄ has a drawback that its charge / discharge voltage is as low as about 3.5 V and the energy density is low. Therefore, LiCoPO ₄ , LiNiPO _{4, and the} like have been proposed as phosphoric acid-based positive electrode materials that can realize a high charge / discharge voltage. However, the present situation is that a sufficient capacity is not obtained even in lithium ion secondary batteries using these positive electrode materials.

Therefore, LiVOPO ₄ has been proposed as a phosphoric acid-based positive electrode material that realizes a high charge / discharge voltage and provides a sufficient capacity (Patent Document 1).

However, in a battery provided with a positive electrode using LiVOPO ₄ obtained by the method described in Patent Document 1, sufficient cycle characteristics cannot be obtained.

JP 2004-303527 A

  The present invention has been made in view of the above-described problems of the prior art, and provides a positive electrode active material, a positive electrode, and a lithium ion secondary battery that can provide sufficient capacity and good cycle characteristics. Objective.

In order to achieve the above object, the positive electrode active material according to the present invention has a half-width of the diffraction peak of the (200) plane of LiVOPO ₄ having a triclinic crystal structure of 0.114 ° to 0.175 °. And an average primary particle diameter is 0.07 micrometer or more and 0.6 micrometer or less, It is characterized by the above-mentioned.

  According to the present invention, it is possible to realize sufficient capacity as compared with the conventional case and good cycle characteristics as compared with the conventional case. Although the reason for this is not necessarily clear, it can be considered as follows.

The full width at half maximum of the diffraction peak of the (200) plane in the vicinity of 2θ = 29.6 ° of the diffraction pattern of LiVOPO ₄ having a triclinic crystal structure reflects the crystallinity and crystallite size of the positive electrode active material. The smaller the value, the higher the crystallinity and the larger the crystallite size, and the larger the half width, the lower the crystallinity and the smaller the crystallite size. Therefore, when the half-value width of the diffraction peak on the (200) plane is 0.114 ° or more, the crystallite size tends to be small enough to obtain a high capacity, and when the half-value width is 0.175 ° or less, charge discharge It is considered that good cycle characteristics can be realized because the crystallinity is stable to a certain extent and stable against repeated Li insertion and desorption. Further, when the average primary particle diameter is 0.07 μm or more, the specific surface area is relatively small, so that the influence of the reaction between the surface of the positive electrode active material and the electrolytic solution is small, and good cycle characteristics tend to be obtained. When the thickness is 0.6 μm or less, the diffusion distance of lithium ions in the positive electrode active material is shortened, so that a sufficient capacity tends to be obtained.

  From the above, it is sufficient when the half width of the diffraction peak of (200) plane is 0.114 ° or more and 0.175 ° or less and the average primary particle size is 0.07 μm or more and 0.6 μm or less. It is considered that it is possible to obtain a capacity and to have a good cycle characteristic.

Moreover, it is preferable that the half width of the diffraction peak of the (002) plane of LiVOPO ₄ having a triclinic crystal structure is 0.118 ° or more and 0.185 ° or less. Thereby, a favorable cycle characteristic is realizable. When the half width of the diffraction peak of the (002) plane near 2θ = 22.4 ° is 0.118 ° or more, the crystallite size tends to be small enough to obtain a high capacity, and the half width is 0.185 ° or less. In this case, it is considered that the crystallinity of the positive electrode active material is higher and sufficient capacity can be obtained and better cycle characteristics can be realized even when repeated charge and discharge are performed.

As a result of intensive studies, the inventors have found that there is a close correlation between the half-value widths of the diffraction peaks of the (200) plane and (002) plane of LiVOPO ₄ having a triclinic crystal structure, and the capacity and cycle characteristics. Found that there is. The reason for this is considered that the (200) plane and the (002) plane tend to be easily affected by the crystallinity particularly in the firing step, pulverization step, classification step and the like.

  In addition, the positive electrode according to the present invention includes a current collector and the positive electrode active material, and includes a positive electrode active material layer provided on the current collector, whereby a sufficient capacity can be obtained and good. Cycle characteristics can be obtained.

  Moreover, the lithium ion secondary battery which concerns on this invention can provide sufficient capacity | capacitance by providing the said positive electrode, and can acquire favorable cycling characteristics.

  According to the present invention, it is possible to provide a positive electrode active material, a positive electrode, and a lithium ion secondary battery that can obtain good cycle characteristics.

It is a schematic cross section of the lithium ion secondary battery according to the present embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

<Lithium ion secondary battery>
The lithium ion secondary battery according to this embodiment will be briefly described with reference to FIG.

  The lithium ion secondary battery 100 mainly includes a laminate 30, a case 50 that accommodates the laminate 30 in a sealed state, and a pair of leads 60 and 62 connected to the laminate 30.

The laminated body 30 is configured such that the positive electrode 10 and the negative electrode 20 are disposed to face each other with the separator 18 interposed therebetween. The positive electrode 10 is a product in which a positive electrode active material layer 14 is provided on a positive electrode current collector 12. The negative electrode 20 is a product in which a negative electrode active material layer 24 is provided on a negative electrode current collector 22. The positive electrode active material layer 14 and the negative electrode active material layer 24 are in contact with both sides of the separator 18. Leads 60 and 62 are connected to the end portions of the positive electrode current collector 12 and the negative electrode current collector 22, respectively, and the end portions of the leads 60 and 62 extend to the outside of the case 50.
<Positive electrode active material>
Then, the positive electrode active material which concerns on this embodiment is demonstrated.

In the positive electrode active material according to this embodiment, the half-value width of the diffraction peak of the (200) plane of LiVOPO ₄ having a triclinic crystal structure is 0.114 ° or more and 0.175 ° or less, and average primary particles The diameter is 0.07 μm or more and 0.6 μm or less. Furthermore, it is more preferable that the half width of the diffraction peak on the (002) plane is 0.118 ° or more and 0.185 ° or less.

  The half width of the diffraction peak reflects the crystallinity and crystallite size of the positive electrode active material. The smaller the half width, the higher the crystallinity and the larger the crystallite size, and the larger the half width, the lower the crystallinity and the smaller the crystallite size. There is a relationship between the crystallite size that provides a sufficient capacity, and a positive electrode active material that is stable against repeated charging and discharging and has a high degree of crystallinity. It is considered that the characteristics can be realized.

  A method for calculating the half width of the positive electrode active material can be obtained by a powder X-ray diffraction method. The crystal structure is identified from the X-ray diffraction pattern, the diffraction peak of (200) plane near 2θ = 29.6 ° having the crystal structure of triclinic crystal, and the diffraction of (002) plane near 2θ = 22.4 °. The full width at half maximum can be obtained from each peak.

  The calculation method of the average primary particle diameter of the positive electrode active material is as follows. First, the positive electrode active material particles are observed with a scanning electron microscope, and 100 or more primary particles are imaged. After calculating the area of each particle of the obtained image, the particle diameter is converted to the equivalent circle diameter, and the average value thereof may be the primary particle diameter.

<Method for producing positive electrode active material>
Although the manufacturing method of a positive electrode active material is not specifically limited, It is known that it can synthesize | combine by a solid-phase synthesis, a hydrothermal synthesis, the carbothermal reduction method etc. Below, the manufacturing method of the positive electrode active material using the hydrothermal synthesis method which concerns on this embodiment is demonstrated.

<Hydrothermal synthesis method>
The manufacturing process of the hydrothermal synthesis method described in the present embodiment includes a raw material preparation process, a hydrothermal synthesis process, a drying process, and a firing process. However, you may implement a baking process, without performing a drying process. You may implement a grinding | pulverization process and a classification process as needed after a baking process.

  In the raw material preparation step, a lithium source, a vanadium source, a phosphorus source, and water are stirred and mixed to prepare a mixed solution. In the raw material preparation step, it is preferable to mix a lithium source, a vanadium source, a phosphorus source and water at the same time. Moreover, you may add a reducing agent as needed.

The lithium source is, for example, selected from the group consisting of Li ₂ CO ₃ , LiF, LiNO ₃ , LiOH, LiCl, LiBr, LiI, Li ₂ SO ₄ , Li ₃ PO _4, CH ₃ COOLi, and hydrates thereof. One kind or two or more kinds can be used. In particular, when a water-soluble lithium salt is used, the discharge capacity of the lithium ion secondary battery tends to be improved. Examples of the water-soluble lithium salt include LiNO ₃ , LiOH, LiCl, LiI, Li ₂ SO ₄ and CH ₃ COOLi, and hydrates thereof.

As the phosphorus source, for example, at least one selected from the group consisting of H ₃ PO ₄ , NH ₄ H ₂ PO ₄ and (NH ₄ ) ₂ HPO ₄ can be used. Two or more phosphorus sources may be used in combination.

As the vanadium source, for example, any of metal vanadium, V ₂ O ₃ , V ₂ O _5, or NH ₄ VO ₃ can be used. Two or more vanadium sources may be used in combination.

The mixing ratio of the lithium source, the vanadium source and the phosphorus source is such that the ratio of the number of moles of lithium contained in the lithium source, the number of moles of vanadium contained in the vanadium source, and the number of moles of phosphorus contained in the phosphorus source is 1: 1: It may be adjusted to be 1. That is, the molar ratio of Li, V and P in the mixture may be adjusted so as to be the stoichiometric ratio of LiVOPO ₄ (1: 1: 1). Note that the blending ratio does not necessarily satisfy the above stoichiometric ratio. For example, in order to prevent the loss of Li in the finally obtained active material, a large amount of lithium source may be blended. That is, the molar ratio of Li, V and P in the mixture may be deliberately shifted from 1: 1: 1.

No particular limitation is imposed on the reducing agent, for example, hydrazine _{(NH 2 NH 2 · H 2} O) or hydrogen peroxide _(H 2 _{O 2)} or the like can be used.

  In the hydrothermal synthesis step, first, the above-described lithium source, phosphate source, vanadium source, water, and reducing agent are put into a reaction vessel (for example, an autoclave) having a function of heating and pressurizing the inside. An aqueous solution in which is dispersed is prepared. Subsequently, the reaction vessel is sealed and heated while pressurizing the mixture, thereby causing a hydrothermal reaction to proceed in the mixture. In addition, what is necessary is just to adjust suitably the time which heats a mixture, pressurizing according to the quantity of a mixture.

  What is necessary is just to heat at about 80-300 degreeC in a drying process. As a drying method, oven drying, spray dryer, flash jet dryer or the like can be used.

  The heat treatment method of the firing step is arbitrary, and for example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln, or the like can be used. The heat treatment is usually divided into three parts of temperature rise, maximum temperature hold, and temperature drop, and the steps of temperature rise, maximum temperature hold, and temperature drop may be repeated twice or more. Further, a crushing step that means eliminating aggregation to such an extent that the secondary particles are not destroyed may be sandwiched between the heat treatments.

  Although the atmosphere of a baking process is not specifically limited, It is preferable that it is an air atmosphere. On the other hand, you may carry out in argon atmosphere, oxygen atmosphere, nitrogen atmosphere, or those mixed atmosphere.

  In the pulverization step, for example, a planetary ball mill or a jet mill can be used as a pulverization method. By the pulverization, the primary particles or the secondary particles are micronized. In addition, you may implement a grinding | pulverization process at the time of producing the positive electrode active material layer of a lithium ion secondary battery. In the manufacturing process of the positive electrode active material layer 14, a slurry prepared from an active material, a conductive additive, a binder, a solvent, and the like is applied on the positive electrode current collector 12 and dried to form the positive electrode active material layer 14. Moreover, you may grind | pulverize the mixture of a positive electrode active material and a conductive support agent in a grinding | pulverization process. Further, the slurry itself may be pulverized.

In the classification step, coarse particles and fine particles can be removed by classifying the product obtained in the firing step or the product obtained in the pulverization step. The classification has advantages such as that drying is not necessary and scale-up is easy, and the dry method is preferable to the wet method. Examples of the dry classifier include a vibration sieve machine, an ultrasonic vibration sieve machine, a cyclone, a micron, a separator, and a high-precision airflow classifier. Moreover, you may repeat a classification process in multiple times as needed.
<Positive electrode>
Subsequently, the positive electrode 10 according to the present embodiment will be described.

  As the positive electrode current collector 12 of the positive electrode 10, for example, an aluminum foil or the like can be used. The positive electrode active material layer 14 contains at least the positive electrode active material according to the present embodiment and a conductive additive. The positive electrode active material layer 14 may include a binder that binds the positive electrode active material and the conductive additive.

  Examples of the conductive aid include carbon materials such as carbon blacks, metal powders such as copper, nickel, stainless steel, and iron, a mixture of carbon materials and metal powders, and conductive oxides such as ITO.

  The binder is not particularly limited as long as the positive electrode active material and the conductive additive can be bound to the positive electrode current collector 12, and a known binder can be used. Examples thereof include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and vinylidene fluoride-hexafluoropropylene copolymer.

  The ratio of the positive electrode active material, the conductive additive, and the binder of the positive electrode active material layer 14 is not particularly limited, but the electrode density tends to decrease when the ratio of the positive electrode active material is small, and the ratio of the positive electrode active material is 80% by weight or more. Is preferred.

  Such a positive electrode 10 is prepared by a known method, for example, a positive electrode active material, a conductive additive and a binder, and a solvent corresponding to the type thereof, for example, N-methyl-2-pyrrolidone, N, N-dimethyl in the case of PVDF. The slurry can be produced by applying a slurry added to a solvent such as formamide on the surface of the positive electrode current collector 12 and drying it.

<Negative electrode>
As the negative electrode current collector 22, a copper foil or the like can be used. Moreover, as the negative electrode active material layer 24, the thing containing a negative electrode active material, a conductive support agent, and a binder can be used. It does not specifically limit as a conductive support agent, A carbon material, a metal powder, etc. can be used. As the binder used for the negative electrode, fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) can be used.

As the negative electrode active material, carbon materials such as graphite and non-graphitizable carbon, metals that can be combined with lithium such as Al, Si and Sn, and amorphous materials mainly composed of oxides such as SiO ₂ and SnO ₂ Examples thereof include particles containing a compound, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), and the like.

  The negative electrode 20 may be manufactured by adjusting the slurry and applying it to the negative electrode current collector 22 in the same manner as the positive electrode 10.

<Electrolyte>
The electrolytic solution is not particularly limited. For example, in the present embodiment, an electrolytic solution containing a lithium salt in an organic solvent can be used. Examples of the lithium _salt, LiPF _6, LiClO 4, salts of LiBF ₄ or the like can be used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together.

  Preferable examples of the organic solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate. These may be used alone or in combination of two or more at any ratio.

  The separator 18 is a monolayer of a film made of polyethylene, polypropylene or polyolefin, a stretched film of a laminate or a mixture of the above resins, or at least one constituent material selected from the group consisting of cellulose, polyester and polypropylene. The fiber nonwoven fabric which consists of can be used.

  The case 50 seals the laminated body 30 and the electrolytic solution therein. The case 50 is not particularly limited as long as it can prevent leakage of the electrolytic solution to the outside and entry of moisture and the like into the lithium ion secondary battery 100 from the outside. For example, a metal laminate film can be used. .

  The leads 60 and 62 are made of a conductive material such as aluminum.

  This positive electrode active material can also be used as an electrode material for electrochemical elements other than lithium ion secondary batteries. As such an electrochemical element, a lithium ion secondary battery other than a lithium ion secondary battery such as a metal lithium secondary battery (an electrode including the positive electrode active material particles of the present invention as a positive electrode and metal lithium as a negative electrode) is used. Examples thereof include secondary batteries and electrochemical capacitors such as lithium capacitors.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
[Preparation of positive electrode active material]
V ₂ O ₅ , LiOH.H ₂ O and H ₃ PO ₄ were weighed so as to have a molar ratio of about 1: 2: 2, poured into distilled water, and stirred with a magnetic stirrer for 1 hour. Hydrazine monohydrate (NH ₂ NH ₂ .H ₂ O) was added dropwise little by little with vigorous stirring, and the mixture was further stirred for 1 hour to prepare a raw material. Thereafter, the mixed solution was transferred to a glass container for autoclave. The vessel was sealed and heated at 160 ° C. for 8 hours with stirring to perform hydrothermal synthesis. The obtained paste was dried in an oven at 100 ° C. for 12 hours. The obtained dry powder was pulverized with a mortar and then baked in the box furnace at 650 ° C. for 4 hours in the air.

The obtained positive electrode active material was subjected to composition analysis by an inductively coupled plasma method (hereinafter, ICP method), and as a result, it was confirmed that the composition was LiVOPO ₄ .

  The obtained positive electrode active material, acetylene black as a conductive auxiliary agent, and ketjen black are weighed at a weight ratio of 80: 5: 5, put in a container, and pulverized by a planetary ball mill at a rotational speed of 550 rpm. For 10 minutes.

About the mixture of the obtained positive electrode active material and conductive support agent, the identification and the half value width of the crystal structure were calculated | required by the powder X ray diffraction method. Using “UltimaIV” manufactured by Rigaku Corporation as an X-ray diffractometer, the measurement was performed under the following measurement conditions.
[Measurement condition]
Filter: Ni
Target: Cu Kα 1.54060Å
X-ray output setting: 40kV-40mA
Slit: Divergence 1/2 °, scattering 1/2 °, light receiving 0.15mm
Scanning speed: 2 ° / min
Sampling width: 0.02 °
The crystal structure was confirmed to be triclinic LiVOPO ₄ , and the half value width of the diffraction peak of the (200) plane at around 2θ = 29.6 ° was 0.164 °, and further, around 2θ = 22.4 °. The half-value width of the diffraction peak on the (002) plane was 0.173 °.

  The positive electrode active material particles subjected to the pulverization treatment were observed with a scanning electron microscope, and the average primary particle diameter was determined by the above-described method, which was 0.31 μm.

[Production of evaluation cell]
A mixture of the positive electrode active material and conductive additive of Example 1 and polyvinylidene fluoride (PVDF, Kureha Chemical KF7305) as a binder in a weight ratio of 90:10 was mixed with N-methyl- A slurry was prepared by dispersing in 2-pyrrolidone (NMP). This slurry was applied onto an aluminum foil as a current collector, dried, and then rolled to produce a positive electrode on which a positive electrode active material layer was formed.

  Next, artificial graphite (FSN manufactured by BTR) and N methylpyrrolidone (NMP) 5 wt% solution of polyvinylidene fluoride (PVdF) as a negative electrode were mixed so that the ratio of artificial graphite: polyvinylidene fluoride = 93: 7 was obtained. A slurry paint was prepared. The negative electrode was produced by apply | coating a coating material to the copper foil which is a collector, and drying and rolling.

A positive electrode and a negative electrode were laminated with a separator made of a polyethylene microporous film interposed therebetween to obtain a laminate (element body). This laminate was placed in an aluminum laminate pack. As the electrolytic solution, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7, and LiPF ₆ was dissolved as a supporting salt to a concentration of 1 mol / L.

  The above electrolyte was poured into an aluminum laminate pack containing the laminate, and then vacuum-sealed to produce an evaluation cell of Example 1.

[Measurement of battery characteristics]
The evaluation cell of Example 1 was charged at a constant current of up to 4.3 V at 25 ° C. with a current value of 18 mA / g and then discharged at a constant current of 2.8 V at a current value of 18 mA / g. At this time, the discharge capacity of Example 1 was 131 mAh / g (initial discharge capacity). A cycle test was repeated for 100 cycles of this charge / discharge cycle. When the initial discharge capacity of the evaluation cell of Example 1 was 100%, the discharge capacity after 100 cycles was 92.8%. Hereinafter, the ratio of the discharge capacity after 100 cycles when the initial discharge capacity is 100% is referred to as a capacity maintenance rate. A high capacity retention rate indicates that the battery is excellent in charge / discharge cycle durability.

(Example 2)
A positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared in the same manner as in Example 1 except that the rotational speed of the pulverization treatment by the planetary ball mill was 520 rpm, and the (200) plane and (002) ) The half width of the diffraction peak of the surface and the average primary particle diameter were determined, and the evaluation cell was produced and the battery characteristics were evaluated. The results are shown in Table 1.

(Example 3)
Except that the rotation speed of the grinding process by the planetary ball mill is 480 rpm, the grinding time is 20 minutes, and the powder remaining on the sieve is used after the grinding process by the vibration sieve process for 10 minutes using the sieve having an opening of 20 μm. In the same manner as in Example 1, a positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared, and the half-value width and average primary particle diameter of diffraction peaks on the (200) plane and (002) plane were determined and evaluated. Cell production and battery characteristic evaluation were performed. The results are shown in Table 1.

Example 4
Example 1 except that the firing temperature of the dry powder was 640 ° C., the pulverization time with a planetary ball mill was 20 minutes, and the powder that passed through the sieve was vibrated using a sieve with an opening of 20 μm after the pulverization step. A positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared in the same manner as described above, and the half-value width and average primary particle size of diffraction peaks of the (200) plane and (002) plane were determined, and the evaluation cell And battery characteristics were evaluated. The results are shown in Table 1.

(Example 5)
Example 1 except that the firing temperature of the dry powder was 640 ° C., the pulverization time with a planetary ball mill was 30 minutes, and the powder that passed through the sieve was vibrated using a sieve having an opening of 20 μm after the pulverization step. A positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared in the same manner as described above, and the half-value width and average primary particle size of diffraction peaks of the (200) plane and (002) plane were determined, and the evaluation cell And battery characteristics were evaluated. The results are shown in Table 1.

(Example 6)
A positive electrode active material and a mixture of a positive electrode active material and a conductive additive were prepared in the same manner as in Example 1 except that powder that passed through a sieve by vibration sieving using a sieve having an aperture of 53 μm was used after the pulverization step. Then, the half-value width and average primary particle diameter of diffraction peaks of the (200) plane and the (002) plane were determined, and an evaluation cell was prepared and battery characteristics were evaluated. The results are shown in Table 1.

(Example 7)
The positive electrode active material, the positive electrode active material, and the conductive auxiliary agent were used in the same manner as in Example 1 except that the powder remaining on the sieve was vibrated for 10 minutes using a sieve having an opening of 20 μm after the pulverization step. A half-width and an average primary particle diameter of diffraction peaks on the (200) plane and the (002) plane were obtained, and evaluation cells were prepared and battery characteristics were evaluated. The results are shown in Table 1.

(Example 8)
In the same manner as in Example 1, except that the firing temperature of the dry powder was set to 660 ° C. and the powder remaining on the sieve was subjected to vibration sieving for 10 minutes using a sieve having an opening of 20 μm after the pulverization step. A mixture of the active material, the positive electrode active material, and the conductive additive is prepared, and the half-value width and average primary particle diameter of the diffraction peaks of the (200) plane and the (002) plane are obtained, and the evaluation cell is manufactured and the battery characteristics are evaluated. went. The results are shown in Table 1.

Example 9
Example, except that after the pulverization step, the sieve was passed by a vibration sieve treatment using a sieve with an opening of 45 μm, and the powder remaining on the sieve by a vibration sieve treatment for 10 minutes using a sieve with an opening of 20 μm was used. In the same manner as in No. 1, a positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared, and the half-value width and average primary particle size of the diffraction peaks on the (200) plane and (002) plane were determined for evaluation. Cell preparation and battery characteristic evaluation were performed. The results are shown in Table 1.

(Example 10)
Example 1 except that the firing temperature of the dry powder was 640 ° C., the pulverization time with a planetary ball mill was 30 minutes, and the powder that passed through the sieve was vibrated using a sieve having an aperture of 53 μm after the pulverization step. A positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared in the same manner as described above, and the half-value width and average primary particle size of diffraction peaks of the (200) plane and (002) plane were determined, and the evaluation cell And battery characteristics were evaluated. The results are shown in Table 1.

(Comparative Example 1)
A positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared in the same manner as in Example 1 except that the rotational speed of the pulverization treatment by the planetary ball mill was 600 rpm, and the (200) plane and (002) ) The half width of the diffraction peak of the surface and the average primary particle diameter were determined, and the evaluation cell was produced and the battery characteristics were evaluated. The results are shown in Table 1.

(Comparative Example 2)
The dried powder was fired at a temperature of 640 ° C., the rotational speed of the pulverization process by the planetary ball mill was 570 rpm, the pulverization time was 20 minutes, and the powder passed through the sieve by the vibration sieve process using a sieve with an opening of 20 μm after the pulverization process. A positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared in the same manner as in Example 1 except that they were used, and the half-value width and average primary of diffraction peaks on the (200) plane and the (002) plane were prepared. The particle diameter was determined, and an evaluation cell was prepared and battery characteristics were evaluated. The results are shown in Table 1.

(Comparative Example 3)
The dry powder was fired at a temperature of 640 ° C., the rotational speed of the grinding process with a planetary ball mill was 600 rpm, and the powder passed through the sieve by vibration sieve treatment using a sieve with an opening of 20 μm was used after the grinding process. In the same manner as in Example 1, a positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared, and the half-value width and average primary particle diameter of diffraction peaks on the (200) plane and (002) plane were determined and evaluated. Cell production and battery characteristic evaluation were performed. The results are shown in Table 1.

(Comparative Example 4)
Implemented except that the firing temperature of the dry powder was 640 ° C., the rotational speed of the grinding process with a planetary ball mill was 600 rpm, and the powder that passed through the sieve was vibrated using a sieve with an opening of 45 μm after the grinding process. In the same manner as in Example 1, a positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared, and the half-value width and average primary particle diameter of diffraction peaks on the (200) plane and (002) plane were determined and evaluated. Cell production and battery characteristic evaluation were performed. The results are shown in Table 1.

(Comparative Example 5)
Implemented except that the firing temperature of the dry powder was 640 ° C., the rotational speed of the grinding process by the planetary ball mill was 600 rpm, and the powder that passed through the sieve was vibrated using a sieve with an opening of 53 μm after the grinding process. In the same manner as in Example 1, a positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared, and the half-value width and average primary particle diameter of diffraction peaks on the (200) plane and (002) plane were determined and evaluated. Cell production and battery characteristic evaluation were performed. The results are shown in Table 1.

(Comparative Example 6)
The dry powder firing temperature was set to 660 ° C., the rotation speed of the grinding process by the planetary ball mill was set to 480 rpm, and the powder remaining on the sieve was used after the grinding process by a vibration sieve process for 10 minutes using a sieve having an opening of 20 μm. Except for the above, a positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared in the same manner as in Example 1, and the half width of the diffraction peaks on the (200) plane and (002) plane and the average primary particle diameter The cell for evaluation and battery characteristic evaluation were performed. The results are shown in Table 1.

(Comparative Example 7)
Example 1 except that the firing temperature of the dry powder was set to 660 ° C., the powder remaining on the sieve was used by vibration sieving for 10 minutes using a sieve having a mesh size of 20 μm, without performing a pulverization treatment with a planetary ball mill. A positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared in the same manner as described above, and the half-value width and average primary particle size of diffraction peaks of the (200) plane and (002) plane were determined, and the evaluation cell And battery characteristics were evaluated. The results are shown in Table 1.

(Comparative Example 8)
The firing temperature of the dry powder is 660 ° C., the pulverization process is not performed with a planetary ball mill, the sieve is passed through a vibration sieve process using a sieve with an opening of 53 μm, and the vibration is performed for 10 minutes using a sieve with an opening of 20 μm. A positive electrode active material and a mixture of the positive electrode active material and a conductive additive were prepared in the same manner as in Example 1 except that the powder remaining on the sieve by the sieving treatment was used, and the (200) plane and (002) The full width at half maximum of the diffraction peak of the surface and the average primary particle diameter were determined, and an evaluation cell was prepared and battery characteristics were evaluated. The results are shown in Table 1.

  As is clear from Table 1, the half width of the diffraction peak of the (200) plane of the positive electrode active materials of Examples 1 to 10 is 0.114 ° to 0.174 °, and the average primary particle size is 0.07 μm. It was confirmed that the thickness was 0.60 μm or less. Moreover, it was confirmed that the initial discharge capacity of the evaluation cells of Examples 1 to 10 is 128 mAh / g or more and the cycle characteristics are 90.1% or more. Furthermore, it was confirmed that the half value width of the diffraction peak of the (002) plane of the positive electrode active materials of Examples 1 to 4 and 6 to 9 was 0.185 ° or less, and the cycle characteristics were 92.1% or more. . Moreover, although the initial discharge capacity of the cells for evaluation of Comparative Examples 1 to 5 was 123 mAh / g or more, it was confirmed that the cycle characteristics were 85% or less. The cycle characteristics of the evaluation cells of Comparative Examples 6 to 8 were 93% or more, but the initial discharge capacity was confirmed to be 107 mAh / g or less.

DESCRIPTION OF SYMBOLS 10 ... Positive electrode, 20 ... Negative electrode, 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 18 ... Separator, 22 ... Negative electrode collector, 24 ... Negative electrode active material layer, 30 ... Laminate, 50 ... Case, 60 62 ... Lead, 100 ... Lithium ion secondary battery.

Claims (4)

Half-width of the diffraction peak of the (200) plane of the LiVOPO ₄ having a crystal structure of triclinic is at 0.17 4 ° below 0.114 ° or more and an average primary particle diameter of more than 0.07 .mu.m 0.6 .mu.m A positive electrode active material characterized by: 2. The positive electrode active material according to claim 1, wherein the half width of the diffraction peak of the (002) plane of LiVOPO ₄ having the triclinic crystal structure is 0.118 ° or more and 0.185 ° or less.   A positive electrode comprising a current collector and a positive electrode active material layer comprising the positive electrode active material according to claim 1 or 2 and provided on the current collector.   A lithium ion secondary battery comprising the positive electrode according to claim 3.

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